The statements in this section merely provide background information related to the present disclosure and may not constitute the prior art.
As multimedia technologies are developed in rapid progress, demand for quality multimedia data including audio, image, and video is increased. Accordingly, for meeting the demand to transmit, store, and retrieve such multimedia data within a limited network environment, international standards are being set up for high efficiency video compression. Specifically, in case of videos, ISO/IEC JTC1/SC29MPEG group and ITU-T VCEG group have created H.264/AVC MPEG-4 Part.10 standard, which attempts to achieve a high compression efficiency by using various prediction encoding methods such as variable block size motion estimation and compensation, intra prediction encoding, etc.
The prediction encoding is an effective method to reduce correlations in existence between data and it is widely used for compressing various types of data. Especially, because a list0 motion vector and a list1 motion vector, which are motion vectors of a current block for two reference pictures in B picture, have a high correlation with motion vectors of adjacent blocks, it is possible to first calculate a prediction value or predicted motion vector (PMV) for a motion vector of a current block by using motion vectors of adjacent blocks and then encode not the true values of the list0 motion vector and the list1 motion vector of the current block but just a differential value or differential motion vector (DMV) relative to the prediction value and thereby substantially reduce the bit quantity to improve the coding efficiency.
Generally, for the purpose of effective compression in the encoding of a motion vector using such a predicted motion vector, more accurately predicted motion vectors proportionally improve the coding efficiency. Therefore, a possible way of improving the efficiency of the predicted encoding is not only to involve motion vectors of the spatially adjacent blocks but also to generate a finite number of predicted motion vectors including temporally, spatially, or the motion vectors of spatio-temporally adjacent blocks or different motion vectors calculated from their combinations and use the most appropriate selection therefrom for the predicted encoding of the motion vectors.
In this occasion, to correctly reconstruct the original motion vector from the prediction based encoded motion vectors, it is necessary to know which one of the finite number of the predicted motion vectors was used. The simplest motion vector prediction encoding method for the task is to additionally encode information on the correct predicted value used to perform the prediction encoding of the motion vectors. Alternatively, to reduce the bit quantity required to encode additional information for indicating such selection of the predicted motion vector, the current H.264/AVC standard uses medians of respective horizontal components and vertical components of the list0 and list1 motion vectors contained in the adjacent blocks (at left, upper, and upper right sides of the current block) as the predicted motion vectors for the predicted encoding of the motion vectors. This method determines a predetermined prediction value calculating means, such as a default means of a median, commonly recognized in an image encoding apparatus and an image decoding apparatus and produces the prediction value (predicted motion vector) using the commonly recognized prediction value calculating, to thereby obviate the need for additionally encoding information on the used prediction motion vector. The conventional method of preparing the predefined prediction value calculating means is only as good as saving an additional information transmission about identifying a motion vector used as the predicted motion vector, but is still deficient because the predicted motion vector that is actually the used median is not the best predicted motion vector to minimally generate the bit quantity required for encoding the differential motion vector.